1. Field of the Invention
The present invention relates to an angular velocity measuring apparatus including a vibration type gyroscope.
2. Related Art Statement
Recently, in a vehicle control system utilizing a body rotation speed feedback system, a vibration type gyroscope has been proposed to be used as a rotation speed sensor. The vibration type gyroscope is an angular velocity sensor utilizing a coriolis force which is produced by a rotation of a vibrating element. The vibrating element is vibrated electrically by supplying a driving signal thereto, and at the same time, a vibration induced by a coriolis force is detected to measure an angular velocity of the rotational movement. In such a system, a direction in which driving wheels are directed is detected by a rotation angle of a steering wheel. At the same time, an actual rotation speed of a vehicle body is detected by the vibration type gyroscope. Then, the driving direction denoted by the steering wheel is compared with the direction obtained from the actual rotation speed to derive a difference, and wheel torque and driving angle are corrected in accordance with the thus detected difference to control the vehicle body stably.
In the vibration type gyroscope, the vibrating element is installed within a package or vessel such as can-package. The can-package is installed within a housing together with a necessary circuit, and the housing is provided on the vehicle body. In this case, after securing a vibration element and a semiconductor integrated circuit chip to a supporting substrate, the substrate is secured to a base of the can-package by means of conductor pins.
For instant, in Japanese Patent Application Laid-open Publication Kokai 2000-9476, a vibration element of tuning fork type is fixed on a supporting substrate and the supporting substrate is installed within a package together with a swing-protection member which serves to prevent undesired swinging movement of the vibration element when unintentional vibration or impact is applied to the vibration element. In this manner, the vibration element can be protected against damage.
Since a space in which the vibration type gyroscopes is arranged in a vehicle is limited, it is required to reduce a surface area of the package as well as a height of the package. However, there has not been developed sufficiently effective measure for miniaturizing the package without affecting a performance of the gyroscope.
The present invention has for its object to provide an angular velocity measuring apparatus utilizing a vibration type gyroscope including a vibration element and a supporting substrate installed within a package, in which a size of the package can be miniaturized without affecting a performance of the vibration type gyroscope.
According to a first aspect of the invention, an angular velocity measuring apparatus for detecting a rotational angular velocity about a rotation axis includes:
a vibration element;
a vibration element supporting member for supporting the vibration element;
a circuit board for supporting the vibration element by means of the supporting member; and
a semiconductor integrated circuit chip for controlling signals for the vibration element.
The semiconductor integrated circuit chip is mounted on the circuit board by flip-chip bonding, and the vibration element is mounted on the semiconductor integrated circuit chip by means of the supporting member.
Upon manufacturing the angular velocity measuring apparatus having the above mentioned unique structure, after mounting the semiconductor integrated circuit onto the circuit board by means of the flip chip bonding, the vibration element is mounted on a flat top surface of the semiconductor integrated circuit chip by means of the supporting member. Then, a size of the angular velocity measuring apparatus can be reduced greatly without affecting the vibration element, driving system for the vibration element and a signal processing system for processing the signals supplied to and from the vibration element.
In a preferable embodiment of the angular velocity measuring apparatus according to the first aspect of the present invention, the vibration element is arranged to extend on a given plane substantially perpendicular to a rotation axis of the vibration element.
The arrangement of the vibration element along the given plane does not strictly mean that the vibration element is formed to extend on a single surface, because the vibration element has a finite thickness. Usually the vibration element may be provided within a space having a height of about 1 mm on the given plane.
Furthermore, it is not always necessary that said given plane is set to be completely perpendicular to the rotation axis and may be inclined with respect to a plane perpendicular to the rotation axis due to a tolerance. Usually, said given plane may be inclined with respect to the real perpendicular plane by an angle not larger than 5xc2x0. Such a vibration element is generally called a laterally placed vibration element. The present invention can provide a remarkable improvement in reducing a size of the package for such a laterally placed vibration element.
In a preferable embodiment of the angular velocity measuring apparatus according to the first aspect of the invention, the semiconductor integrated circuit chip is arranged to extend substantially in parallel with the vibration element. In this case, the vibration element and semiconductor integrated circuit chip are preferably overlapped with each other viewed in a direction of the rotation axis. Then, a height and a lateral dimension of the can-package can be effectively reduced.
According to the invention, any kind of the semiconductor integrated circuit chip for controlling a driving signal supplied to the vibration element and a detection signal generated from the vibration element may be used. Particularly, it is preferable to use ASIC (Application Specified Integrated Circuit).
When the semiconductor integrated circuit chip is mounted on the circuit board by the flip chip bonding and the vibration element is mounted on the semiconductor integrated circuit chip by means of the supporting member, the thus assembled vibration element, supporting member, circuit board and semiconductor integrated circuit chip may be accommodated within a can-package.
According to a second aspect of the invention, an angular velocity measuring apparatus for detecting a rotational angular velocity about a given rotation axis includes:
a vibration element;
a vibration element supporting member for supporting the vibration element;
a semiconductor integrated circuit chip for controlling signals for the vibration element;
a ceramic circuit board for supporting the vibration element by means of the supporting member; and
a lid hermetically secured to the ceramic circuit board to constitute a space;
wherein at least the vibration element and vibration element supporting member are installed within the space.
In this manner, when the vibration element is mounted on the ceramic circuit board by means of the vibration element supporting member, a standoff from a mother board which is required in the known can-package can be dispensed with, and therefore a height of the package after installing the vibration element can be further reduced. Furthermore, in the can-package, conductor pins have to be inserted into through-holes formed in a base of the can-package and then the conductor pins have to be soldered to the circuit board. In case of using the ceramic circuit board according to the second aspect of the present invention, it is no more necessary to use the conductor pins, and the semiconductor integrated circuit chip can be connected to an external circuit by soldering conductors to contact lands provided on a rear surface of the ceramic circuit board. Therefore, undesired damage and breakage of conductor pins can be avoided. When impact is applied to the package from the external, the conductor pins might be twisted and an error signal might be generated. According to the second aspect of the invention, the generation of such an error signal can be also suppressed.
According to a third aspect of the invention, an angular velocity measuring apparatus for detecting a rotational angular velocity about a given rotation axis includes:
a vibration element;
a vibration element supporting member for supporting the vibration element;
a circuit board for supporting the vibration element by means of the supporting member;
a semiconductor integrated circuit chip for controlling signals for the vibration element;
a can-package having a can-package base and a can-package lid hermetically welded to the can-package base to constitute a space; and
a plurality of conductor pins extending into the space through the can-package base and electrically connected to the circuit board;
wherein the vibration element is mounted on one surface of the circuit board by means of the vibration element supporting member, the semiconductor integrated circuit chip is mounted on the other surface of the circuit board by bare-die-bonding and is connected to the circuit board by bonding wires, the circuit board and the conductor pins secured to the can-package base are fixed by a silver paste.
Since the semiconductor integrated circuit chip is mounted on the rear surface of the circuit board by means of the bare-die-bonding and is connected to the circuit board by bonding wires, the potting process for protecting the semiconductor integrated circuit chip and bonding wires is no more necessary. Furthermore, since the semiconductor integrated circuit chip is provided between the circuit board and the base of the can-package, the semiconductor integrated circuit chip can be effectively prevented from being damaged by unintentional impact during a manufacturing process prior to welding the lid to the can-package in an air-tight manner. Moreover, since the circuit board is connected to the conductor pins by means of the silver paste, a washing process which is required in the case of soldering may be dispensed with.